1. Field of the Invention
This invention relates to computer system configurations and, more particularly, to arrangements and connections of computer system circuit boards.
2. Description of the Related Art
Computer systems are typically available in a range of configurations which may afford a user varying degrees of reliability, availability and serviceability (RAS). In some systems, reliability may be paramount. Thus, a reliable system may include features designed to prevent failures. In other systems, availability may be important and so systems may be designed to have significant fail-over capabilities in the event of a failure. Either of these types of systems may include built-in redundancies of critical components. In addition, systems may be designed with serviceability in mind. Such systems may allow fast system recovery during system failures due to component accessibility. In critical systems, such as high-end servers and some multiple processor and distributed processing systems, a combination of the above features may produce the desired RAS level.
Various drawbacks may be associated with systems that provide high levels of RAS capability. For example, to provide redundancy, additional duplicate system components are usually necessary. Depending on the number of additional components, there may be an increase in overall system size. In some systems, it may be difficult to cool the additional system components and thus additional air plenums may be necessary to provide an adequate flow of cooling air. The additional plenums may also increase system size.
Many systems use a back plane or centerplane to distribute the various signals and power to the system circuit boards and components. However, the centerplane may complicate system cooling by blocking airflow through the system boards. Further, if the centerplane fails, it may not be replaceable without bringing down the system.
In addition, as the size and complexity of a system increases, other components of the system may also be difficult to service. For example, if a component fails, it is sometimes necessary to remove operative components to access the failed component. In such a case, it may be necessary to shut down one or more subsystems, which may mean losing partial or whole system functionality.